Motion in One Dimension

An electron with initial velocity [itex] v_{x}_{o} = 1.0 \times 10^{4} [/itex] meters/sec enters a region where it is electrically accelerated. It emerges with a velocity [itex] v_{x} = 4.0 \times 10^{6} [/itex] meters/sec. What was its acceleration, assumed constant? The accelerated region is 1 cm. So acceleration is defined as [itex] \frac{\Delta v}{\Delta t} [/itex]. How would I use the fact that the accelerated region is 1 cm long?